Read registry backups as UTF8

[BiosSystem]

Load-RegistryBackupFromFile read with no -Encoding, so Windows PowerShell 5.1 fell back to the ANSI codepage for a file with no BOM. Registry data holds non-ASCII - an accented user profile path being the obvious case - and this is the restore path, so a corrupted read writes mangled values back to the system rather than merely failing.

Latent, not active

SaveToFile writes with -Encoding UTF8, which in 5.1 emits a BOM, so WinSwift's own backups happened to read correctly. The read was working by accident.

Anything produced elsewhere has no BOM: PowerShell 7 writes UTF8 without one by default, and the restore dialog explicitly invites users to supply files ("Only use backup files generated by WinSwift" is a warning, not an enforcement). Confirmed the failure before fixing it:

SaveToFile writes a BOM : True
BOM file reads correctly with no -Encoding                PASS
no-BOM file reads correctly with no -Encoding             FAIL
   got: C:\Users\José\AppData\Señor
no-BOM file reads correctly WITH -Encoding UTF8           PASS

The .reg reader is deliberately untouched

Get-RegFileOperations also reads with no -Encoding, and it must stay that way. Regedit writes .reg as UTF-16LE with a BOM - verified, the repo's files start FF FE - which Get-Content already detects. Forcing UTF8 there would corrupt all 100-plus registry files. A test pins that so nobody applies the same fix twice.

Verified

WinSwift-written backup keeps accents                     PASS
BOM-less backup keeps accents (was corrupting)            PASS
   got: C:\Users\José\AppData\Señor
missing file still throws                                 PASS
invalid JSON still throws                                 PASS
reg file still parses (Add_All_Folders_Under_This_PC.reg) PASS
   operations parsed: 13

Error handling is unchanged: a missing file and invalid JSON still throw as before.

Static validation passes (112 files), standalone rebuilt and parse-checked.

Four other reads still lack -Encoding - RemoveApps, LoadAppPresetsFromJson, LoadAppsDetailsFromJson, LoadAppsFromFile - all reading Apps.json, which is pure ASCII today. Lower risk than the restore path and left for a separate change.